A rotation angle detector comprises a shaft part having a torsion bar, a rotation angle
detection part for detecting the rotation angle of the shaft part, and a torque
detection part for detecting the twist angle of the torsion bar. The detection accuracies
of the rotation angle detection part and the torque detection part themselves
can be enhanced by mutually utilizing the results of respective detections. Thereby,
the detector can detect the rotation angle and the twist angle of a rotating body
which does multiple rotations with high accuracy and high resolution power.